Oxidative stress-induced cell death occurs during ischemia/reperfusion (I/R) injury and following toxicant exposure in the kidney, resulting in acute renal failure (ARF). Consequences of oxidative stress include peroxidation of membrane phospholipids and organelle dysfunction. Using renal proximal tubular cells and isolated endoplasmic reticulum (ER) and mitochondria, our laboratory has shown that calcium-independent phospholipase A2-gamma (iPLA2-gamma) is localized to the ER and mitochondria. Inhibition of this enzyme results in increased lipid peroxidation, mitochondria! dysfunction, and cell death following oxidant exposure. These results are consistent with the hypothesis that iPLA2-gamma is cytoprotective through its ability to remove oxidized membrane fatty acids, thereby preventing further lipid peroxidation, mitochondrial dysfunction and cell death. However, this hypothesis has not been tested in an in vivo model. We propose to investigate this hypothesis using iPLA2-gamma knock-out mice. Specific Aim 1 will determine the role of iPLA2-gamma in the maintenance of oxidized and non-oxidized renal phospholipids and in the protection of kidney and mitochondrial function in wild-type mice and knock-out mice during aging. Specific Aim 2 will elucidate the cytoprotective role of iPLA2-gamma under an acute oxidant stress and bilateral renal I/R injury in wild-type and knock-out mice by examining renal oxidized and non-oxidized phospholipids and the extent of kidney and mitochondrial dysfunction and recovery over time. Understanding the protective role of JPLA2- gamma in renal function may lead to future therapies to prevent or treat ARF. Acute renal failure is a major cause of hospitalizations in the United States. One cause is oxidative stress that can occur as a result of ischemia followed by reperfusion of the kidneys following injury, disease, or exposure to certain toxicants. These experiments are designed to investigate how a phospholipase A2 (iPLA2-gamma) may be protective against acute renal failure with the hope that improved treatments may be developed in the future.